What exactly is adrenaline and cortisol and how do they work?

What are they composed of? How do they work? What are the positive and negative effects? It seems to me that if adrenaline and cortisol could make humans so powerful, why isn't it in constant use? Or at least used more often? Are there doented abnormalities that make the adrenal gland produce more adrenaline and cortisol, or possibly produce them with higher quality? Please tell me as much as you know about any and all of these subjects. Expert opinion and speculation is appreciated.